There are more than 5,000 varieties of mushrooms, of which about 50-100 are known to be toxic and only 200-300 are known to be safely edible. The majority of toxic mushrooms cause mild-to-moderate self-limited gastroenteritis. A few species may cause severe or even fatal reactions. The major categories of poisonous mushrooms are described in Table II-40. Amanita phalloides and other amatoxin-containing mushrooms are discussed.

The various mechanisms thought to be responsible for poisoning are listed in Table II-40. The majority of toxic incidents are caused by GI irritants that produce vomiting and diarrhea shortly after ingestion.

The amount of toxin varies considerably among members of the same species, depending on local geography and weather conditions. In most cases, the exact amount of toxic mushroom ingested is unknown because the victim has unwittingly added a toxic species to a meal of edible fungi.

The various clinical syndromes are described in Table II-40. These presentations can often be recognized by the time to onset of symptoms.

1. If onset is within 6 hours, the likely categories will be GI irritants, cholinergic syndrome, hallucinogenic, isoxazole syndrome, immunohemolytic, allergic pneumonitis, or allenic norleucine class.
2. Mushrooms that cause symptoms with onset from 6 to 24 hours after ingestion include those containing amatoxins or monomethylhydrazine and those causing erythromelalgia.
3. Onset of symptoms more than 24 hours after ingestion suggests poisoning by the orellanines that cause kidney damage, mushrooms causing rhabdomyolysis, or mushrooms causing delayed CNS toxicity.
4. Mushrooms in the coprine category do not cause symptoms unless the patient ingests alcohol. This disulfiram-like effect can occur from 30 minutes to as long as 5 days after ingestion.

May be difficult because the victim may not realize that the illness was caused by mushrooms, especially if symptoms are delayed after ingestion. If leftover mushrooms are available, obtain assistance from a mycologist through a local university or mycologic society. However, be aware that the mushrooms brought for identification may not be the same as those that were ingested.

History is key to determining the category of toxic mushroom. It is important to get a description of the mushroom and the environment from which it was obtained. Was the mushroom cooked or eaten raw? Were several types of mushrooms ingested? What was the time of ingestion in relation to the onset of symptoms? Was alcohol ingested after the mushrooms were eaten? Is everyone who ate the mushroom ill? Are those who did not eat the mushroom also ill? Were the mushrooms eaten several times? Were they stored properly? The suspected mushroom can be kept in a paper bag in the refrigerator labeled “do not eat” in case further identification is required.

1. Specific levels. Qualitative detection of the toxins of most mushroom species are not routinely available.
2. Other useful laboratory studies include CBC, electrolytes, glucose, BUN, creatinine, liver aminotransferases, and prothrombin time (PT/INR). Obtain a methemoglobin level using co-oximetry if gyromitrin-containing mushrooms are suspected or the patient is cyanotic. Obtain a chest radiograph if allergic pneumonitis syndrome is suspected, and serial creatine kinase (CK) levels for suspected rhabdomyolysis.

1. Emergency and supportive measures
   1. Treat hypotension from gastroenteritis with intravenous crystalloid solutions. Acute renal injury can occur from severe vomiting and diarrhea resulting in significant volume loss, especially with amatoxin poisoning.
   2. Treat agitation, hyperthermia, rhabdomyolysis, and seizures if they occur. Antiemetics should be given to patients with nausea and/or vomiting.
   3. Monitor patients for 12-24 hours for delayed-onset gastroenteritis associated with amatoxin or monomethylhydrazine poisoning.
   4. Monitor renal function for 1-2 weeks after suspected Cortinarius species ingestion, or 2-4 days after Amanita smithiana ingestion. Provide supportive care, including hemodialysis if needed, for renal dysfunction.
2. Specific drugs and antidotes
   1. For seizures following monomethylhydrazine poisoning, treat with IV benzodiazepines (lorazepam or diazepam), and give pyridoxine, 25 mg/kg IV; treat methemoglobinemia with methylene blue, 1-2 mg/kg IV.
   2. For muscarine intoxication with cholinergic symptoms, give atropine, 1-2 mg IV for adults and 0.02 mg/kg IV for children.
   3. Allergic pneumonitis may benefit from corticosteroid administration.
   4. Treat amatoxin-type poisoning as described on.
   5. For coprine-associated disulfiram-like reaction, treat with fluids (see Disulfiram,).
3. Decontamination. If the mushroom is potentially toxic or unidentified, administer activated charcoal orally if conditions are appropriate (see Table I-37).
   1. Charcoal is probably not warranted after a trivial ingestion (eg, a lick or a nibble) of an unknown mushroom by a toddler.
   2. Repeat-dose activated charcoal may be helpful after amatoxin ingestion.
4. Enhanced elimination. There is no accepted role for these procedures.